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      <a id="clfilt"></a>
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      <a id="IndexClfilt" class="indexterm"></a>
      <div class="refnamediv">
        <h2>
          <span class="refentrytitle">clfilt</span>
        </h2>
        <p>clfilt — 
      Implements low-pass and high-pass filters of different styles.
          </p>
      </div>
      <div class="refsect1">
        <a id="idp94532240"></a>
        <h2>Description</h2>
        <p>
       Implements the classical standard analog filter types: low-pass and high-pass. They are implemented with the four classical kinds of filters: Butterworth, Chebyshev Type I, Chebyshev Type II, and Elliptical.  The number of poles may be any even number from 2 to 80.
    </p>
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      <div class="refsect1">
        <a id="idp94593200"></a>
        <h2>Syntax</h2>
        <pre class="synopsis">ares <span class="command"><strong>clfilt</strong></span> asig, kfreq, itype, inpol [, ikind] [, ipbr] [, isba] [, iskip]</pre>
      </div>
      <div class="refsect1">
        <a id="idp94595408"></a>
        <h2>Initialization</h2>
        <p>
      <span class="emphasis"><em>itype</em></span> -- 0 for low-pass, 1 for high-pass.
    </p>
        <p>
      <span class="emphasis"><em>inpol</em></span> -- The number of poles in the filter. It must be an even number from 2 to 80.
    </p>
        <p>
      <span class="emphasis"><em>ikind</em></span> (optional) -- 0 for Butterworth, 1 for Chebyshev Type I, 2 for Chebyshev Type II, 3 for Elliptical. Defaults to 0 (Butterworth)
    </p>
        <p>
      <span class="emphasis"><em>ipbr</em></span> (optional) -- The pass-band ripple in dB. Must be greater than 0. It is ignored by Butterworth and Chebyshev Type II. The default is 1 dB.
    </p>
        <p>
      <span class="emphasis"><em>isba</em></span> (optional) -- The stop-band attenuation in dB. Must be less than 0. It is ignored by Butterworth and Chebyshev Type I. The default is -60 dB.
    </p>
        <p>
      <span class="emphasis"><em>iskip</em></span> (optional) --  0 initializes all filter internal states to 0. 1 skips initialization. The default is 0.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp94602608"></a>
        <h2>Performance</h2>
        <p>
      <span class="emphasis"><em>asig</em></span> -- The input audio signal.
    </p>
        <p>
      <span class="emphasis"><em>kfreq</em></span> -- The corner frequency for low-pass or high-pass.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp94605280"></a>
        <h2>Examples</h2>
        <p>
      Here is an example of the clfilt opcode as a low-pass filter. It uses the file <a class="ulink" href="examples/clfilt_lowpass.csd" target="_top"><em class="citetitle">clfilt_lowpass.csd</em></a>.

      </p>
        <div class="example">
          <a id="idp94607168"></a>
          <p class="title">
            <strong>Example 120. Example of the clfilt opcode as a low-pass filter.</strong>
          </p>
          <div class="example-contents">
            <p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
            <pre class="programlisting">
<span class="csdtag">&lt;CsoundSynthesizer&gt;</span>
<span class="csdtag">&lt;CsOptions&gt;</span>
<span class="comment">; Select audio/midi flags here according to platform</span>
-odac     <span class="comment">;;;RT audio out</span>
<span class="comment">;-iadc    ;;;uncomment -iadc if RT audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o clfilt_lowpass.wav -W ;;; for file output any platform</span>
<span class="csdtag">&lt;/CsOptions&gt;</span>
<span class="csdtag">&lt;CsInstruments&gt;</span>

<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">ksmps</span> <span class="op">=</span> 32
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="ohdr">0dbfs</span> <span class="op">=</span> 1

<span class="oblock">instr</span> 1	<span class="comment">; white noise</span>

asig <span class="opc">rand</span> 0.5
<span class="opc">outs</span> asig, asig

<span class="oblock">endin</span>

<span class="oblock">instr</span> 2	<span class="comment">; filtered noise </span>

asig <span class="opc">rand</span> 0.9
<span class="comment">; Lowpass filter signal asig with a </span>
<span class="comment">; 10-pole Butterworth at 500 Hz.</span>
a1 <span class="opc">clfilt</span> asig, 500, 0, 10
   <span class="opc">outs</span> a1, a1

<span class="oblock">endin</span>

<span class="csdtag">&lt;/CsInstruments&gt;</span>
<span class="csdtag">&lt;CsScore&gt;</span>

<span class="stamnt">i</span> 1 0 2
<span class="stamnt">i</span> 2 2 2
<span class="stamnt">e</span>

<span class="csdtag">&lt;/CsScore&gt;</span>
<span class="csdtag">&lt;/CsoundSynthesizer&gt;</span>
</pre>
          </div>
        </div>
        <p><br class="example-break" />
    </p>
        <p>
      Here is an example of the clfilt opcode as a high-pass filter. It uses the file <a class="ulink" href="examples/clfilt_highpass.csd" target="_top"><em class="citetitle">clfilt_highpass.csd</em></a>.

      </p>
        <div class="example">
          <a id="idp94612560"></a>
          <p class="title">
            <strong>Example 121. Example of the clfilt opcode as a high-pass filter.</strong>
          </p>
          <div class="example-contents">
            <p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
            <pre class="programlisting">
<span class="csdtag">&lt;CsoundSynthesizer&gt;</span>
<span class="csdtag">&lt;CsOptions&gt;</span>
<span class="comment">; Select audio/midi flags here according to platform</span>
-odac     <span class="comment">;;;RT audio out</span>
<span class="comment">;-iadc    ;;;uncomment -iadc if RT audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o clfilt_highpass.wav -W ;;; for file output any platform</span>
<span class="csdtag">&lt;/CsOptions&gt;</span>
<span class="csdtag">&lt;CsInstruments&gt;</span>

<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">ksmps</span> <span class="op">=</span> 32
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="ohdr">0dbfs</span> <span class="op">=</span> 1

<span class="oblock">instr</span> 1	<span class="comment">; white noise</span>

asig <span class="opc">rand</span> 0.6
     <span class="opc">outs</span> asig, asig

<span class="oblock">endin</span>

<span class="oblock">instr</span> 2	<span class="comment">;filtered noise</span>

asig <span class="opc">rand</span> 0.7
<span class="comment">; Highpass filter signal asig with a 6-pole Chebyshev</span>
<span class="comment">; Type I at 20 Hz with 3 dB of passband ripple.</span>
a1 <span class="opc">clfilt</span> asig, 20, 1, 6, 1, 3
   <span class="opc">outs</span> a1, a1

<span class="oblock">endin</span>

<span class="csdtag">&lt;/CsInstruments&gt;</span>
<span class="csdtag">&lt;CsScore&gt;</span>

<span class="stamnt">i</span> 1 0 2
<span class="stamnt">i</span> 2 2 2
<span class="stamnt">e</span>

<span class="csdtag">&lt;/CsScore&gt;</span>
<span class="csdtag">&lt;/CsoundSynthesizer&gt;</span>
</pre>
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        <p><br class="example-break" />
    </p>
      </div>
      <div class="refsect1">
        <a id="idp94616896"></a>
        <h2>Credits</h2>
        <p>Author: Erik Spjut</p>
        <p>New in version 4.20</p>
      </div>
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